package data_structure.leetcode;

import data_structure.entry.ListNode;

public class Solution21 {

    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        if (l1.val > l2.val) {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        } else {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }
    }

    public ListNode mergeTwoListsIR(ListNode l1,ListNode l2){

        ListNode preHead=new ListNode(-1);
        ListNode pre=preHead;
        while(l1!=null&&l2!=null) {

            if (l1.val <= l2.val) {
                pre.next = l1;
                l1 = l1.next;
            } else {
                pre.next = l2;
                l2 = l2.next;
            }
            pre = pre.next;
        }
        return pre.next;
    }
}
